1. Field of the Invention
The invention relates generally to a method and device for machining hard materials such as ceramics and glass, and more specifically to the use of a special broach for smoothing an orifice surface of a work piece consisting of a hard material.
2. Information Disclosure Statement
The method and devices for machining orifices into hard materials such as ceramics and glass are well known in the art. Perhaps the most common method involves ultra-sound machining. As discussed in U.S. Pat. No. 5,140,773, ultrasonic machine tools conventionally have a machining head connected to a piezoelectric transducer and a grindstone such as a diamond for boring or polishing. In operation, the machine head is rotated by a motor while the piezoelectric transducer ultrasonically vibrates. The top of the tool is then pressed into the work. The piezoelectric transducer causes the tool to vibrate axially and radially on the surface of the work thereby boring it.
The vibrating nature of this boring process creates surface anomalies on the orifice surface. Moreover, in the conventional method of ultrasonic machining, the rigidity of the tool is very low when its diameter is small (for example, less than 1 mm). Lacking rigidity, the tip of the tool tends to bend and slide at the initial stage of the machining when no guide hole is yet formed. Consequently, the tip makes an eccentric rotation on the surface of the work without making a bore. This eccentric rotation adds to the surface anomalies created in ultrasonic machining.
U.S. Pat. No. 5,140,773 offers an improved method and device for making such bores. This patent discloses a method and apparatus for reducing the eccentric rotations present in the initial stages of machining. Although this improves the quality of the orifice surface, the surface anomalies inherent in ultrasonic machining remain.
The traditional method of removing these surface anomalies is to hand file them. To hand finish an orifice surface, the hard work piece is placed under a microscope and a person uses a small file to smooth the anomalies one at a time. This process is extremely tedious, time consuming, and subject to human error and inconsistency. A need therefore exists to remove these surface anomalies in a systematic and expedient manner. The present invention fulfills this need.